Non-aqueous electrolyte secondary batteries, typically including lithium ion batteries, are drawing attention as batteries for electric vehicles and energy storage since they have high specific energy densities. Electric vehicles includes so-called “zero-emission” electric vehicles without engine, hybrid electric vehicles with both an engine and a secondary battery, and plug-in hybrid electric vehicles charged with electricity directly from an electrical grid. Moreover, non-aqueous electrolyte secondary batteries are expected to be used in stationary energy storage systems for smoothly coordinating photovoltaic power generation or wind power generation with an electric power system.
For such various uses, lithium ion batteries are required to have large outputs. That is, in a power source for mobile use, an output performance of 0.1 hour rate or higher is required on startup and shutdown. Moreover, an output performance of 1 to 0.2 hour rate is required in a power source for stationary use for the purpose of interconnection, power backup during power failure, and load leveling. Herein, 1 hour rate represents a rate of charge or discharge when the rated capacity of a lithium ion battery is fully used in one hour. At 0.2 hour rate, a 5 times larger current than at 1 hour rate, and at 0.1 hour rate, a 10 times larger current is charged or discharged.
When a current value of charge or discharge of the lithium ion battery is increased, a current per unit area of an electrode (that is, current density) is increased, which lowers a voltage due to reaction resistance, electric resistance, or ion diffusion resistance. In particular, repeating charge-discharge cycles significantly lowers the voltage. This is because particles of a battery active material repeatedly expand and shrink by the charge-discharge cycles, and the electronic network between the particles is gradually cut. It should be noted that a battery active material used in this specification mean a cathode active material or an anode active material.
In order to avoid these problems, attempts to improve the lifetime of the charge-discharge cycles have been made by using a highly adhesive rubber-based binder or adding a conducting material having a minute particle structure such as carbon black (see JP-A-2000-173622, JP-A-2001-155737, JP-T-2009-538495, JP-A-2007-165061, JP-A-2005-190831, JP-A-2005-78933, JP-A-2005-63846, JP-A-2004-288520, and JP-A-2002-260637). The highly adhesive rubber-based binder is for absorbing a change in volume of battery active materials by the flexibility of the binder when particles of the battery active materials expand and shrink. Minute conducting materials such as carbon black is for filling a conducting material between the particles of the battery active materials to maintain the electronic network between the particles by the conducting material even if the volume of the battery active materials is changed.
JP-A-2000-173622 discloses an invention relating to an anode using carbon particles as a conducting material, which support only a metal not forming an alloy with lithium substantially. JP-A-2001-155737 discloses an invention for producing an electrode by using binder for a lithium ion secondary battery electrode including a non-conductive polymer whose surface is covered with a conductive polymer. JP-T-2009-538495 discloses an invention relating to a nanocomposite electrode including an intermediate layer region which electrically conducts with a current collector and a battery active material. JP-A-2007-165061 discloses an invention for adding a powder, or a sphere-like or columnar supporting material powder to the electrode to impart electron conductivity to the electrode. JP-A-2005-190831 discloses an invention relating to an electrode having a layer including an active material with a thickness of 120 to 2000 μm and having a conducting material and a binder with a content rate of 0.5 to 6% by mass of the total mass of the layer including the active material. JP-A-2005-78933 discloses an invention relating to composite particles including battery active material particles, conducting material particles, and binder particles. JP-A-2005-63846 discloses an invention characterized by mixing a battery active material with polymer particles including a conductivity-imparting agent containing conductive carbon and a binder. JP-A-2004-288520 discloses an invention relating to an electrode structure in which a conductive intermediate layer is disposed between a mixture layer and a current collector. JP-A-2002-260637 discloses an invention relating to an anode produced by sintering a layer of a mixture of an active material particles including silicon and a conductive metal powder in a non-oxidizing atmosphere on the surface of a current collector, which is a conductive metal foil having a surface roughness Ra of 0.2 μm or more.
An object of the present invention is to provide a long-life battery including an electrode having an electronic network in the interior, the electronic network unlikely deteriorating after charge-discharge cycles.